What is Salinization?

Soil salinization occurs when water-soluble salts accumulate in the soil to a level that impacts on agricultural production, environmental health, and economics. In the early stages, salinity affects the metabolism of soil organisms and reduces soil productivity, but in advanced stages it destroys all vegetation and other organisms living in the soil, consequently transforming fertile and productive land into barren and desertified lands

Where does it occur?

It is estimated that salinization affects around 3.8 million ha in Europe3. There are different causes of salinization but irrigated areas in particular can be affected by salinization. It is estimated that 25% of irrigated cropland in the Mediterranean area is affected by moderate to high salinization leading to moderate soil degradation4. Projected temperature increases and changes in precipitation characteristics in the Mediterranean are only likely to enhance the problem of salinization.

Map: Saline (EC > 4 dScm-1 within 100 cm soil depth) and sodic (Na/T > 6% within 100 cm soil depth) soils as primary and secondary limitations to agricultural use and areas of seawater intrusion in the European Union5

What causes it?

Natural processes

The accumulation of salts in the soil can occur through natural processes such as physical or chemical weathering and transport from parent material, geological deposits or groundwater. It can also occur due to parent rock constituents, such as carbonate minerals and/or feldspars or as a result of the one-time submergence of soils under seawater. Sea level rise also induces seepage into areas lying below sea level. In arid areas, saline soils are formed due to evapotranspiration and lack of rainfall to flush the soils. Finally, wind in coastal areas can blow moderate amounts of salts inland.

Human activities

Human activities can cause salinization through the use of salt-rich irrigation water, which can be exacerbated by overexploitation of coastal groundwater aquifers causing seawater intrusion, or due to other inappropriate irrigation practices, and/or poor drainage conditions. The excessive use of water for irrigation in dry climates, with heavy soils, causes salt accumulation because they are not washed out by rainfall. The process occurs in cultivated areas where irrigation is associated with high evaporation rates and a clay texture of the soil. The practice of waterlogging without adequate drainage has also become a serious cause of soil salinization. Waterlogged soils prevent leaching of the salts imported by the irrigation water.

Rainwater harvesting: A network of gutters channels rainwater to a metal tank, and is later used for irrigation

Biological soil amendments: Mycorrhiza supplement in the form of grey aggregates used during tomato transplantation

Green manuring: Sorghum seeded in June and incorporated in the ground as in August using a tille

Case Study Experiment

How does it interact with other soil threats?

As salinity is responsible for the structural collapse of soil aggregates into their components it is closely linked to other soil degradation issues. Salinity is often associated with prolonged wetness and lack of surface cover and therefore increases the vulnerability of soils to erosion. Salt interacts with animals and plants, changing the ecological health of land, streams and estuaries. The greatest threat to biodiversity is from the loss of habitat both on land and in water.

How does it affect soil functions?

Biomass production - soils in salt-affected landscapes are less fertile and produce less biomass than non-saline soils resulting in less soil organic carbon (SOC) and in turn more erosion, which further accentuates SOC losses due to the dominance of plant inputs in the accumulation of organic matter.

Storing/filtering/transforming - salinization affects a series of environmental interactions leading to reduced water infiltration and retention resulting in increased water runoff and erosion